In the electrical relay and contactor art the coil or solenoid typically is wound on a molded plastic bobbin. One type of bobbin that has been used extensively includes a thick flange at one end of the cylindrical position of the bobbin. This flange has a groove or pocket therein that extends transversely or circumferentially across the flange and radially from the periphery of the flange inwardly to the cylindrical body portion of the bobbin. The groove may be somewhat pie shaped. The lead wire of the coil passes through the groove with a transverse as well as radial component of direction. Terminals extend outwardly from each side of the groove. An opening or slit in the top wall of the flange allows the lead wire to pass from the first terminal on one side of the groove, through the groove with transverse, or circumferential, as well as radial components of direction, and then onto and around the cylindrical body portion of the bobbin. The coil then may be wound in a conventional manner onto the body portion between the end flanges of the bobbin. The free end of the coil wire then is secured to the other terminal on the other side of the radially extending groove in the thick flange. The lead wire in the groove usually is somewhat slack in order to avoid stresses therein. Coils and bobbins constructed in this general mannerr are shown in the following U.S. Pat. Nos. 3,177,294--Muszynski et al; 3,230,489--Weyrich; 3,525,965--Sparling; 3,230,490--Johnson; and 4,041,430--Hrynewycz.
It has been found that in coils wound in this manner the lead wire that is within the groove in an end flange is subject to vibrations, especially when alternating current is coupled to the coil. The vibrations have caused the lead wire in the groove to break. It has become common practice to fill the radially extending groove with a potting material in order to hold the wire in a fixed position and avoid breaks therein. This practice has been successful to accomplish its desired purpose, but it adds potting material and at least one additional step to the manufacturing procedure. In volume production, the additional material and handling amounts to a significant added cost.